1. Field of the Invention:
The present invention relates to novel fluorine-containing elastomers and more particularly to fluorine-containing elastomers best characterized by excellent compatibility with fillers, high thermal resistance and good oil resistance, whose composition is the chemically grafted copolymer consisting of fluorine-containing polymeric segments and organopolysiloxane segments.
2. Description of Prior Art:
Rubber-like materials having the three distinct characteristic properties of high thermal resistance, good oil resistance, and satisfactory low temperature properties are of great demand in market. The prior art of fluorine-containing elastomers, such copolymers as, for example, vinylidene fluoride-hexafluoropropylene, tetrafluoroethylene-propylene and terafluoroethylene-perfluoroalkylperfluorovinyl ether have excellent thermal resistance and oil resistance, however, do not have satisfactory low temperature properties. On the other hand, silicone rubbers having such main chain as, for example, dimethylsiloxane and methylphenylsiloxane exhibit excellent thermal resistance, together with satisfactory low temperature properties, but oil resistance of the said rubbers is unfortunately not up to the required standard.
To overcome this aspect of difficulty, fluorosilicone rubbers consisting of methyl trifluoropropylsiloxane as main chain and that fluorophosphazane rubbers have been developed, but they are still too expensive enough to fill the market needs.
As is well known for those skilled in this art, blending of silicone rubbers having excellent heat resistance and satisfactory low temperature properties and fluorine-containing rubber has been extensively studied in order to incorporate both advantageous properties and to avoid the disadvantages each component thereof. This approach, however, has not been successful because of the lack of compatibility of the rubber toward each other, the difference in machanism and rate of curing, and the difference in viscosities of each polymeric component, so that the said blended compound is still not in a position of practical use.
Fluorocarbon rubbers are generally not highly compatible with inorganic fillers, such as for example, carbon black, clay and talc. When forced to mix, rubber-like elasticity is surely lost. Therefore, although fluorocarbon rubbers have excellent thermal resistance and oil resistance, it can not be used for oil-sealing nor other similar purposes. Moreover, fluorocarbon rubbers exhibit relatively high viscosity owing to the inflexibility of the main chain. In addition, nonstickiness and lubricance of the fabricated articles are not always sufficient.